Preheating system for plywood hot press machine

ABSTRACT

A system for operation in conjunction with an existing temperature controlling system for a plywood press to momentarily &#39;&#39;&#39;&#39;override&#39;&#39;&#39;&#39; the latter system to permit applying a higher than normal temperature to the press platens to impart initial, rapid heating to the plywood panel thereon. The temperature controller system re-assumes control of the press temperature after the momentary rise of the platen temperature. Accordingly, the time required to heat and cure a plywood panel is reduced with increased productivity of the plywood press being realized.

United States Patent 191 Fails [451 Jan. 15, 1974 PREHEATING SYSTEM FOR PLYWOOD HOT PRESS MACHINE Inventor: Julius G. Fails, 911 Fairview Dr.,

.SPPi fid O eg- 9 4 Filed: Mar. 10, 1971 Appl. N0.: 122,742

U.S. Cl. 100/93 P, 100/38, 100/43, 156/359, 156/583, 425/143 Int. Cl. B02c 11/08, B30b 15/34 Field of Search 100/93 P, 92, 48, 100/38, 43, 51; 156/359, 583; 18/17 H, 17 C, 17 P, 16 P, HM, 30 CM; 425/143 References Cited UNITED STATES PATENTS 12/1947 Stocker /93 P X 2,646,105 7/1953 Langer 100/93 P Primary Examiner-Peter Feldman Attorney-James D. Givnan, Jr.

[57] ABSTRACT A system for operation in conjunction with an existing temperature controlling system for a plywood press to momentarily override the latter system to permit applying a higher than normal temperature to the press platens to impart initial, rapid heating to the plywood panel thereon. The temperature controller sys tem re-assumes control of the press temperature after the momentary rise of the platen temperature. Accordingly, the time required to heat and cure a plywood panel is reduced with increased productivity of the plywood press being realized.

2 Claims, 1 Drawing Figure HEAT FLOW mimmm 1s m JULIUS G FAILS INVENTOR.

PREHEATING SYSTEM FOR PLYWOOD HOT PRESS MACHINE BACKGROUND OF THE INVENTION The present invention relates generally to heated presses used in the manufacture of plywood for pressing the glued layers of wood together in the presence of heat to form the completed plywood panel. More particularly, the present system provides means for momentarily and automatically raising the temperature of the platens of the press during initial heating of the panels by the press.

In the manufacture of plywood panels each panel, comprising outer face sheets with inner cores or laminates, is subjected to both heat and pressure while in the plywood press. Such pressing is accomplished by a series of movable platens, usually steam heated, which are forcefully urged by hydraulic means into compressing contact with each of the plywood panels in place on the press platens. The heat and pressure, applied for a period of a few minutes, results in the curing of the multiple gluelines or glued surfaces of the panels laminates with the glue forming both a chemical bond with the wood as well as achieving mechanical adhesion with the wood surfaces.

The operating temperatures of a plywood press are variable to best achieve curing of the particular run of plywood panels being pressed. Thickness of the panels will usually vary from one run to another. For example plywood panels comprising seven laminates of wood veneer will require a different press condition than a panel of three laminates. The greater the thickness of a panel being cured the greater the time required to uniformly heat the entire panel to achieve the optimum curing of all the gluelines of the panel.

The present plywood presses have an automatically regulated heat flow (usually steam) to the press with the exhaust flow from the press being monitored by a temperature sensor, which in conjunction with other temperature control means, automatically regulates the heat flow to the press. For a run of panels of a certain thickness existing temperature control means will attempt to maintain a constant temperature in the press platens. At the start of a pressing cycle the platens will be at the desired temperature with the platens temperature being subsequently lowered by heat conduction to the panels. The exhaust flow temperature is thereby decreased which results in a signal to the temperature controller for increased heat flow to the press. One such temperature controller is manufactured and sold by the Foxboro Company of Foxboro, Massachusetts which controller is well known throughout the plywood industry.

In the manufacture of plywood panels it may besaid that the hot pressing operation is the most time consuming operation and hence other associated mill equipment and panel layup is paced by the speed of the plywood press. With presses operating continuously throughout two or three shift working days, during good times, any time savings made in a panel curing cycle becomes significant to production when viewed over a 24 hour period. The present invention reduces the cycling time of a plywood press by momentarily preheating the press platens above an optimum. curing temperature without excessive heat being imparted to the panels being cured.

In a typical cycle of a hot plywood press the temperature of the platens is reduced by conduction of their heat into the panel being pressed. The temperature of the heat flow downstream from each of the platens is accordingly reduced ultimately causing the temperature sensor to transmit a signal for additional heat flow. The instant invention works in conjunction with existing temperature controlling equipment but in distinc tion, provides for heating of the platens to a somewhat higher than normal press operating temperature with heat diffusion in the wooden panel being such as to avoid overheating of the panels surface sheets.

SUMMARY OF THE INVENTION The present invention is directed toward providing a preheating system for plywood presses operable to provide a temporary increase in the press platen temperature to expedite curing of the plywood panel thereon. The elevated platen temperature occurs for a predetermined interval to avoid excessive panel temperature yet accomplish uniform heating of the panel. Components of the present system operate in conjunction with certain press operations to initiate platen preheating at the desired time and further may utilize existing valves and conduits without effecting their normal operation.

An important object of the instant invention is to provide a system for the operation of a valve regulating heat flow to the press to control said valve at intervals to override the presses existing temperature controller. Variation of the temperature of the press platens for intervals above an optimum curing temperature permits reduction in the press cycle of operation and hence increase press production.

A further object is the provision of a preheating system readily adaptable to existing press heating systems wherein, if desired, existing components may be utilized for ease of installation and cost savings.

Another object of the invention is to provide a preheating system for a plywood press timed to press oper ation with adjustable preheating system components enabling the preheating interval to be regulated to suit the panels being pressed.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing the present embodiment of the invention is shown enclosed within closed dashed lines in association with a prior art temperature controlling system shown exteriorly of the dashed lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With continuing reference to the drawing wherein applied reference numerals indicate parts similarly identified in the following specification, the reference numeral 10 indicates generally a typical hot plywood press machine having a series of hollow heated platens 11 upon which plywood panels P are cured. Such presses include a mechanical power source such as hydraulically operated rams 12 which forcefully raise the platens and the plywood panels thereon into alternate compressing contact to imparting heat and pressure to the upper and lower plywood panel surfaces. Each platen 11 in such presses is independently slidably supported for upward travel towards an adjacent platen for heating and pressing of the panel thereon. After a pe riod of a few minutes the press opens to the position shown at which time the panels are removed from their platens and new panels put in place thereon. The load ing and unloading of the press is typically accomplished by additional automatic equipment not important to an understanding of the present invention.

For heating of the platens 11 an outlet manifold 13 extends alongside the series of platens with flexible conduits at 14A-14B providing for a heat flow through each platen. The heat flow exhausts from the platen via the conduits 148 which terminate in communication with a collection pipe 15 for transfer and discharge of the heat flow as indicated by the applied arrow. Heating of the platens may be by steam, the flow of which into manifold 13 is controlled by a flow control valve 16, which in turn is operated by a pneumatic temperature control instrument indicated at 17. One such temperature control instrument widely used with plywood presses is manufactured by The Foxboro Company of Foxboro, Massachusetts. The above-mentioned temperature control instrument as shown includes a temperature sensitive bulb 18 located so as to sense the temperature of the heat flow downstream of the platens. A gas filled conduit at 19 communicates the temperature signal from the bulb 18 to the main temperature controlling instrument 17. The temperature controller instrument 17 is supplied with a pre-set system air pressure via a line 20. A second line at 21 serves to communicate air pressure, as regulated by instrument 17, with a pressure responsive regulator device 22 for operation of a flow control valve 16. Said instrument 17 includes temperature and pressure recorders which indicate on time graduated graphs a continuous record of press operating conditions. Supply line for instru ment 17 is provided with a filter and moisture trap at 23 and an air supply pressure regulator 24.

The temperature controller instrument 17, upon receiving a signal originating at sensor bulb 18 indicating platen temperatures are below a specific temperature, will increase the air pressure in line 21 ultimately resulting in valve 16 being moved towards an open position.

In a typical installation the regulated system pressure to the instrument 17 may be 17 psi with an instrument controlled pressure in line 21 accomplishing the following positions of valve 16:

3 psi initial opening 6 psi one-quarter open 9 psi one-half open 12 psi three-quarters open 15 psi full open The foregoing description is ofa well known temperature controlling system used in conjunction with hot plywood presses. The following description sets forth the present invention providing a preheating system which advantageously utilizes some of the aforementioned components.

Indicated at 28 is a solenoid for operation of an air valve body 29 which is served by a pair of air lines 30 and 31 which terminate in Tees 32 and 33. Accordingly the pre-set system air pressure may be communicated to air line 21 in a manner by-passing the controller 17.

Operation of solenoid 28 and valve 29 is effected by a settable timer mechanism 34 having a load circuit 35, 36 for energizing the coils (not shown) of solenoid 28. A source of electrical power is provided the timer via a conductor 37 provided with a manual system OFF- ON switch 38 and a press actuated switch 40. The

switch 40 is located on the press and closes upon downward activation by a platen 11 as indicated by a dashed line. A secondary source, via a lead 41, is provided the timer 34 for sustaining timer operation and its load circuit energization regardless of opening of switch 40 upon platen movement. A return to ground is provided by line 42.

The press actuated switch 40 may be dispensed with and instead utilization made of switch components in the press electrical component console which normally include circuitry energized upon the press moving toward its open position.

The operation of the preheating system for momentary elevation of the platen temperature is as follows. Prior to closure of the press for curing of a new load of panels solenoid valve 29 will open to admit a pressure increase to the regulator means 22 of flow control valve 16. Air pressure in line 21 is utilized by both the conventional temperature controlling system and the present preheating system with the latter including airlines 30, 31 for bypassing the conventional system.

The open duration of valve 16 will be as determined by the settable timer 34 as the different thicknesses of panels being cured will require different preheating periods. For example, a run of three-quarter inch plywood panels requires a normal platen temperature of approximately 285F. With the present preheating system the platen temperature would be elevated to approximately 305F. with such heating achieved by the full open condition of flow control valve 16. For a run of panels of lesser thickness, for example, fivesixteenths, the normal press temperature would be approximately 270F. with preheating to 290F. Timer operation for this latter example would obviously be of shorter duration than that for the panels of greater thickness.

The duration of timer operation will approximate a minute or two to achieve preheat temperatures desired. In addition to the thickness of the plywood other variables include the temperature of the wood as it comes to the press and ambient air temperature all of which must be taken into consideration in setting of the timer interval.

During the interval the solenoid valve 29 is open system pressure from the source is bypassed around the temperature control mechanism 17 with said pressure ultimately causing the further opening of flow control valve 16.

At times when the preheating system is tie-energized the temperature control mechanism 17 will function in its normal manner to meter system pressure to the regulator 22 of valve 16, with the metering being in response to the signal from the temperature sensor 18 in the exhaust flow from the press.

While I have shown but one embodiment of the invention it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the invention.

Having thus described the invention what is desired to be secured under a Letters Patent is:

l. A preheating system for a plywood press having a series of movable heated platens for the momentary elevation of the press temperature above its normal operating temperature for imparting rapid intial heating to plywood panels being cured on the press platens, said press having a heat flow control valve with regulating means therefor and temperature controlling means associated with the regulating means to automatically control valve operation to maintain a pre-set normal operating temperature, said preheating system momentarily overriding the temperature controlling means and comprising,

valve means in communication with a pressure source and with the regulating means of the heat flow control valve,

a timer mechanism operable for settable timed periods less than the curing cycle of plywood panels and having a load circuit actuating said valve means, and

switch means in circuit with the timer mechanism and with an electrical source said switch means closed upon opening movement of said platens to initiate timer operation energizing its load circuit whereby said valve means is opened for a timed period to open the heat flow control valve for a timed duration overriding the temperature controlling means to preheat momentarily the press platens above their normal operating temperature resulting in a reduction of press cycling time.

2. The preheating system as claimed in claim 1 wherein the temperature controlling means and the regulating means utilize air pressure metered by the former to actuate the heat flow control valve, said preheating system additionally including air lines bypass ing the temperature controlling means, said valve means in communication with said air lines whereby said valve means upon opening serves to communicate full system pressure to the regulating means for opening of said heat flow control valve. 

1. A preheating system for a plywood press having a series of movable heated platens for the momentary elevation of the press temperature above its normal operating temperature for imparting rapid intial heating to plywood panels being cured on the press platens, said press having a heat flow control valve with regulating means therefor and temperature controlling means associated with the regulating means to automatically control valve operation to maintain a pre-set normal operating temperature, said preheating system momentarily overriding the temperature controlling means and comprising, valve means in communication with a pressure source and with the regulating means of the heat flow control valve, a timer mechanism operable for settable timed periods less than the curing cycle of plywood panels and having a load circuit actuating said valve means, and switch means in circuit with the timer mechanism and with an electrical source, said switch means closed upon opening movement of said platens to initiate timer operation energizing its load circuit whereby said valve means is opened for a timed period to open the heat flow control valve for a timed duration overriding the temperature controlling means to preheat momentarily the press platens above their normal operating temperature resulting in a reduction of press cycling time.
 2. The preheating system as claimed in claim 1 wherein the temperature controlling means and the regulating means utilize air pressure metered by the former to actuate the heat flow control valve, said preheating system additionally including air lines bypassing the temperature controlling means, said valve means in communication with said air lines whereby said valve means upon opening serves to communicate full system pressure to the regulating means for opening of said heat flow control valve. 